Upgrade ink version

[cuteolaf]

Due to the changes introduced in Polkadot v0.9.43, E2E tests are failing with substrate contracts node v0.27.0.
The issue is fixed in this PR, but it's not released yet.

So we need to

• Upgrade ink as soon as a new version is released.
• Clarify in the README that we should use substrate contracts node( < v0.27.0) for E2E tests